Dental handpieces, e.g. equipped with a bur, are of common use in dental cabinets. The pneumatic bur, located at the distal free end portion of the handpiece, rotates at high speed under the propelling force of a primary air flow provided by an air turbine, for allowing efficient drilling operations to be performed in the patient's teeth. Cooling of the bur is necessary to prevent the bur and the tooth from becoming too hot under the high velocity friction forces induced therein. The cooling is achieved by means of an atomized water spray which is projected against the tooth and the bur drilling head. The propelling air flow is recovered and discharged. However, the cooling water droplets are expelled into the patient's mouth through the bur head.
An important problem associated with conventional bur units is that the cooling water often develops high counts of microorganisms, particularly anaerobic bacteria, due to water stagnation in the water conduits or tubes feeding, the handpiece. Use of this contaminated water can worsen mouth infections for the patients in the case of pathogenic bacteria colonies, and at least leave a bad taste in the patient's mouth. Quantitatively, the amount of water used by the dental handpiece during dental procedures is very small. Due to this low water flow rate and to the relatively important length of the water lines connected to the dentist's water providing apparatus, water therein is likely to stagnate for a few days, typically for one or two weeks on average, before it is expelled at the outlet for cooling the distal bur head. The medium of the water lines containing stagnating water is thus favourable to bacteria development, and the bacteria count may increase significantly during stagnation time at favourable dental room temperatures. This may result in local infections of a patient's oral cavity upon a portion of the high count bacteria water being expelled into his mouth, especially if the patient has flesh wounds resulting either from the dentist's intervention or other causes.
Chemical compounds can be injected at regular time intervals into the dentist water line network to sterilize the water tubing and eliminate the bacteria formations in the water lines, when water lines are not in operation. However, these cleaning products are likely to--and often do--damage the valves and other parts of the water tubes, especially the rubber gaskets and valves therein, due to their chemical composition. Also, a patient may be contaminated by the often toxic cleaning products if residues of this chemical cleaner remain when the water tubes are not rinsed properly after the cleaning products have been circulated therein. Thus, particular efforts have to be undertaken to both cleanse and rinse the water tubes.
It is known to use sterilized water bags to supply sterile water for dental operations to be pursued without risk of bacterial infection from water tap pathogenic bacteria formations. However, this alternative is much more expensive than using the conventional tap water, and requires that the dentist or dental surgeon connects his dental unit apparatus to such a bag before use, and it is also prone to promoting bacterial formation due to water stagnation in the tubing linking the water bag to the dental handpiece.
U.S. Pat. No. 2,274,893 issued in 1942 to H. Freedman discloses a dental apparatus for feeding a water spray into the mouth of a person. The Freedman apparatus includes a water tube which is equipped at its intermediate portion with a drainage pipe provided with a flap valve. The tube intermediate portion is destined to be positioned lower than the tube proximal inlet and distal outlet extremities, so that gravity forces the water in the pipe down towards the drainage pipe to evacuate same. The flap valve includes a resilient flap which remains opened in an unbiased condition, thus allowing the water to freely flow out into the drainage pipe; and which closes under the pressure differential to block the drainage pipe upon water flowing from the inlet extremity to the outlet extremity. Thus, water back-flow from the distal ejector nozzle into the water tube is allegedly controlled.
A problem with the dental apparatus disclosed in the Freedman apparatus, is that it requires the water tube to be positioned in a particular way, i.e. with its intermediate portion located lower than the remaining segments of the tube. If other segments are lowered under the level of the drainage pipe, then water stagnation is likely to occur. Also, the dental apparatus of the Freedman apparatus is especially adapted for a water spray nozzle of old construction, where the water flow rate is greater than in modern dental handpieces; thus, the purpose of the drainage pipe in the Freedman patent is to prevent water from running back from the outlet nozzle into the tube, and eventually into the water reservoir. It is not adapted to prevent water stagnation, and does not offer any form of continuous water flow in the tube.